Terpenes are a diverse family of compounds with carbon skeletons composed of five-carbon isoprene units. Approximately 20,000 different terpenes and terpenoids (compounds of terpene origin whose carbon skeleton has been altered or rearranged) have been identified to date, representing only a small fraction of the estimated natural variation. Terpenes are commonly isolated from the essential oils of plants. Essential oils often have pleasant tastes or aromas, and they are widely used as flavorings, deodorants, and medicines.
Sesquiterpenes are terpenes with 15 carbon atoms (three isoprene units). The plant kingdom contains the highest diversity of sesquiterpenes. Often they play a role in defense of the plants against pathogens, insects and herbivores and for attraction of pollinating insects.
Valencene (1,2,3,5,6,7,8,8a-octahydro-7-isopropenyl-1,8a-dimethyl-naphthalene) and nootkatone (4,4a,5,6,7,8-hexahydro-6-isopropenyl-4,4-a-dimethyl-2(3H)-naphtalenone) are just two examples of sesquiterpenes that are derived from cyclization of the ubiquitous pyrophosphate intermediate farnesyl diphosphate. Nootkatone is formed by the oxidation of valencene.
Valencene and nootkatone are compounds of natural origin, and are natural constituents of citrus oils, such as orange and grapefruit. Because of its excellent organoleptic qualities and in particular its typical grapefruit taste, nootkatone is a widely used ingredient in perfumery and the flavor industry. Alternatively, nootkatone may be used as an insecticide. Valencene, the starting material for the generation of nootkatone (either biologically or chemically), is also used as a flavorant and fragrance.
Several methods to purify sesquiterpenes, such as valencene and nootkatone, from citrus fruits or to maintain high levels of these sesquiterpenes in citrus fruit extracts have been described in the prior art. These methods are described below.
Japikse et al., in U.S. Pat. No. 4,693,905, claimed a method of extracting concentrated orange flavor and aroma compositions from natural orange essence oil by using a dense solvent gas. Their procedure entailed (a) contacting natural orange essence oil with a solvent gas having a temperature between its critical temperature and 100° C., and having a reduced pressure between about 0.56 and about 1.31 (where reduced pressure is defined as the extraction pressure of the solvent gas divided by its critical pressure), to extract flavor and aroma compounds; (b) separating the solvent gas and dissolved compounds from the remaining undissolved compounds; and (c) separating the dissolved compounds from the solvent gas.
Rich, in U.S. Pat. No. 4,973,485, discloses a method of producing aqueous orange stripper essences and orange stripper oils with high ratios of valencene to the less desirable orange flavor compounds. This procedure involves the following steps: (a) heating an orange fed juice stream to a temperature of 37.7° C. to 71° C.; (b) stripping the heated feed juice with steam at a steam:soluble solids ratio of 0.3 to 1.5, at a temperature of 37.7° C. to 71° C. and at a stripping column pressure of less than 9 inches of Hg, absolute; (c) condensing the stripped volatiles at a temperature of 40.6° C. to −196° C.; (d) centrifuging the condensate in a continuous stacked disk hermetic centrifuge to produce two clear phases; and (e) removing the aqueous orange stripper essence phase.
In U.S. Pat. No. 5,260,086 Downton et al. describe a process for making an aseptic citrus sensible pulp/juice slurry by extracting and removing juice from citrus juice containing sensible pulp. After this process is complete, flavorants, such as valencene are added to make up for those that are lost during this extraction process.
Hiramoto et al., in U.S. Pat. No. 6,495,193 prepares a citrus flavor from a low-boiling part of a cold pressed oil by a hydrate alcohol solvent extraction. To maintain the stability of the flavor, a stabilizing coumarin analogue component is added.
In a US patent application, publication number US 20030185956, Gradley claims a separation method for extracting desired sesquiterpene aroma compounds, such as valencene and nootkatone, from an aqueous phase by separating the aqueous mixture from a water-immiscible hydrophobic phase by means of a hydrophilic membrane and allowing the desired components to move out off the aqueous phase through the membrane and into the hydrophobic phase.
Kotachi et al., in US patent application, publication number 20030203090, teaches of a process for preparing orange oil useful as fragrance or flavor material, by mixing raw material oil containing valencene with a high-boiling solvent having a boiling point exceeding 240° C. under normal pressure, to give a mixture, and fractionally distilling the mixture obtained.
Nootkatone is a high demand, high value flavorant added to many of the commercial soft drinks sold worldwide. Currently, the practice of extracting nootkatone from citrus pulp and rind is considered an expensive and somewhat unreliable process. Nootkatone can be synthesized by the oxidation of valencene. The valencene starting material is expensive and is easily degraded during evaporative heat concentration processes typically used to remove the bulk of water from the feed juice. Thus, current methods to purify valencene from citrus fruits are costly, difficult, and are limited by what the fruit can deliver. Moreover, such methods are vulnerable to interruptions in the supply of citrus fruits, which is dependent on the weather. A frost or hailstorm in a major citrus fruit growing region such as Florida can interrupt the supply. Furthermore, methods to produce nootkatone that consume valencene are quite costly, and thus not commercially desirable. Therefore, there is a need for an alternative means for preparing valencene and nootkatone.